Preparation of 1-alkyl-1,4-dihydro-7-substituted-4-oxo-1,8-naphthyridine-3-carboxylic acids via the 3-carboxaldehyde analogs

ABSTRACT

Process of reacting 1,4-dihydro-4-oxo-7-Q-1,8-naphthyridine (I) with a formylating agent to produce 1,4-dihydro-4-oxo-7-Q-1,8naphthyridine-3-carboxaldehyde II, reacting II with a loweralkylating agent to produce 1-(lower-alkyl)-1,4-dihydro-4-oxo-7Q-1,8-naphthyridine-3-carboxaldehyde (III), and oxidizing III to produce 1-(lower-alkyl)-1,4-dihydro-4-oxo-7-Q-1,8-naphthyridine3-carboxylic acid (IV), where Q is lower-alkyl, loweralkanoyloxymethyl, 4(or 3)-pyridyl or 4(or 3)-pyridyl having one or two lower-alkyl substituents. The final products (IV) are known antibacterial agents, as are the corresponding 7hydroxymethyl compounds which are prepared by hydroylsis of the final products where Q is 7-(lower-alkanoyloxymethyl).

United States Patent [191 Lesher et al.

[111 3,873,554 [451 Mar. 25, 1975 [75] Inventors: George Y. Lesher, Schodack; Monte D. Gruett, East Greenbush, both of NY.

I [73] Assignee: Sterling Drug Inc., New York, NY.

[22] Filed: Mar. 6, 1973 [21] Appl. No.: 338,613

[56] References Cited UNITED STATES PATENTS 12/1965 Lesher 260/2955 B 10/1968 Lesher 260/2955 B OTHER PUBLICATIONS Kittilu, Dimethylformamidc Chemical Uses, E. I. du

Pont de Nemours & Co., Pub1icatj o n, copyright (1967).

. oxo-7-Q-1,S-naphthyridine-3-carboxy1ic acid Klingsberg, Pyridine and Its Derivatives, Part Three, Interscience Publishers, Pages 190-195, 1962. OD 401 K5 C.2. I

Primary ExaminerA1an L. Rotman Attorney, Agent, or Firm-Robert K Bair; B. Woodrow Wyatt 57 ABSTRACT Process of reacting naphthyridine (I) with a formylating agent to produce 1,4-dihydro-4-oxo-7-Q-1,8-naphthyridine-3- carboxaldehyde II, reacting II with a lower-alkylating agent to produce 1-(10wer-a1ky1)-1 ,4-dihydro-4-oxo-7- Q-l,8-naphthyridine-3-carboxa1dehyde (111), and oxidizing III to produce 1-(lower-a1ky1)-l,4-dihydro-4- where Q is lower-alkyl, lower-alkanoyloxymethyl, 4(or 3)-pyridyl or 4(or 3)-pyridy1 having one or two loweralkyl substituents. The final products (IV) are known antibacterial agents, as are the corresponding 7- hydroxymethyl compounds which are prepared by hydroylsis of the final products where Q is 7-(1oweralkanoyloxymethyl).

4 Claims, No Drawings 1,4-dihydro-4-oxo-7-Q-1,8-

PREPARATION OF l-ALKYL-l ,4-DIHYDRO-7-SUBSTITUTED-4-OXO- l,8-NAPHTHYRlDlNE-S-CARBOXYLIC ACIDS VIA THE 3-CARBOXALDEHYDE ANALOGS This invention relates to steps in the process of preparing l,8-naphthyridine-3-carboxylic acids and to compositions used therein.

The invention in a process aspect comprises the combination of the three steps of reacting l,4-dihydro-4- oxo-7-Q-l,8-naphthyridine (l), which is tautomeric with 4-hydroxy-7-Q-1,S-naphthyridine (lA), with a formylating agent to produce 1,4-dihydro-4-oxo-7-Q-1,8- naphthyridine-3-carboxaldehyde (ll), which is tautomeric with 4-hydroxy-7-Q- l ,8-naphthyridine-3- carboxaldehyde (llA), reacting ll (or llA) with a loweralkylating agent to produce dihydro-4-oxo-7-O-l,8-naphthyridine-3- carboxaldehyde (Ill), and reacting lll with an oxidizing agent capable of converting CHO to COOl-l to produce l-( lower-alkyl)-l ,4-dihydro-4-0xo-7-Q- l ,8- naphthyridine-3-carboxylic acid (IV), where Q is lower-alkyl, lower-alkanoyloxymethyl, 4(or 3)-pyridyl or 4-(or 3 )-pyridyl having one or two lower-alkyl substituents. The final products (IV) are known antibacterial agents, as are the corresponding 7-hydroxymethyl compounds which are prepared by hydrolysis of the final products where Q is lower-alkanoyloxymethyl. In addition to said combination of the three steps, other process aspects of the invention are each individual step and the two consecutive combinations of two steps.

The invention in its composition aspect resides in the compounds: l,4-dihydro-4-oxo-7-Q-l ,8-naphthyridine- 3-carboxaldehyde and its tautomeric 4-hydroxy-7-Q- l,8-naphthyridine-3-carboxaldehyde of the respective formulas ll and HA CHO and l-( lower-alkylll, l dihydro-4-oxo-7-Q-l1fl naphthyridine-3-carboxaldehyde of formulalll CHO l III Q, N N

where is lowe r alkyl and Q in each of the formulas ll, 11A and III is defined as hereinabove.

The compounds of formulas ll, HA and III are disclosed and claimed in copending application Ser. No. 453,929, filed Mar. 22, 1974.

The term lower-alkyl. as used herein e g.. as represented by R in formula lll or as a substituent of 4(or 3 )-pyridyl when represented by Q in formulas ll, "A or III, means alkyl radicals having from one to six carbon atoms which can be arranged as straight or branched chains, illustrated by methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, n-amyl, n-hexyl and the like.

The term lower-alkanoyl, as used herein, e.g., in the definition of the Q substituent as loweralkanoyloxymethyl in formulas ll, llA or lll, means alkanoyl radicals having from one to six carbon atoms, including the straightand branched-chain radicals, illustrated by formyl, acetyl, propionyl (propanoyl), butyryl (butanoyl), isobutyryl (2-methylpropanoyl) and caproyl (hexanoyl).

Illustrative of the Q substituent in formulas Ill, lV,

IVA and V where Q is 4(or 3)-pyridyl having one orv two'lower-alkyl substituents are the following: 2-methyl-4-pyridyl, 2,6-dimethyl-4-pyridyl, 3-methyl-4- pyridyl, 2-methyl-3-pyridyl, 6-methyl-3-pyridyl (preferably named 2-methyl-5-pyridyl), 2,3-dimethyl-4- pyridyl, 2,5-dimethyl-4-pyridyl, 2 ethyl-4-pyridyl. 2-isopropyl-4-pyridyl, 2-nbutyl-4-pyridyl, 2-n-hexyl-4- pyridyl, 2,6-diethyl-4-pyridyl, 2,6-diethyl-3-pyridyl. 2,6-diisopropyl-4-pyridyl, 2,6-di-n-hexyl-4-pyridyl and the like. Because of ready availability, ease of preparation and/or high antibacterial activity of the final products, i.e., the l-(lower-alkyl)- l,4-dihydro-7-[mono(or di)-(lower-alkyl)-4-(or naphthyridine-3-carboxylic acids, preferred embodiments of this group are those where 4-(or 3)-pyridyl is substituted by one or two methyls, especially the 2-methyl-4-pyridyl and 2,6-dimethyl-4-pyridyl compounds. Other preferred embodiments are those having unsubstituted-4(or 3)-pyridyl as Q.

As shown above, 1,4-dihydro-7-Q-4-oxol ,8- naphthyridine-3-carboxaldehyde of formula ll is tautomeric with 4-hydroxy-7-Q-1,8-naphtyridine-3- carboxaldehyde of formulalIA. As with all tautomeric systems, the rate of the transformation ll 7- HA and the ratio ll/llA are dependent on the thermodynamic environment, including the state of aggregation; so that measurements by any particular techniques do not necessarily have validity except under the conditions of the measurement, thereby, among other consequences,

.giving rise to problems for any simple designation of the physical embodiments. Thus, measurements of the infrared spectra, in potassium bromide admixture, or in chloroform or mineral oil, indicate existence predominantly as ll and the names of the compounds herein therefore are preferably based on structure ll, although it is understood that either or both structures are comprehended.

The intermediate 1,4-dihydro-4-oxo-7-Q-l ,8- naphthyridines (l) or tautomers (lA) are either known or, where novel, are prepared from known compounds by methods illustrated hereinbelow.

One such method, which is disclosed and claimed in copending application Ser. No. 335,733, filed Feb. 26, 1973, comprises the steps of reacting cyclic alkylidenyl N-(6-Q-2-pyridyl)aminomethylenemalonate, where Q is lower-alkyl, 4(or 3)-pyridyl, or 4(or 3)-pyridyl having one or two lower-alkyl substituents, with an oxidizing agent capable of converting pyridines to pyridine- N-oxides to produce cyclic alkylidenyl N-(6-Q'-l-oxo- -P q l amiaamethylsnemal aataow11 e, is ower-alkyl, l-oxo-4(or 3)-pyridyl or l-oxo-4(or 3)-pyridyl having one or two lower-alkyl substituents, heating said 6-Q'-l-oxo-2-pyridyl compound to produce 1,4- dihydro-4-oxo-7-Q'-1,8-naphthyridine-8-oxide and then converting said 8-oxide to the corresponding 1,4- dihydro-4-oxo-7-Q-l,S-naphthyridine. Illustrations of this method are given below in Examples 64-l 10.

The molecular structures of the composition aspects (II, IIA and III) of our invention were assigned on the basis of evidence provided by infrared, ultraviolet and nuclear magnetic resonance spectra, by chromatographic mobilities, and, by the correspondence of calculated and found values for the elementary analyses for representative examples.

The manner of making and using the instant invention will now be generally described so as to enable a person skilled in the art of chemistry to make and use the same, as follows:

The reaction of 1,4-dihydro-4-oxo-7-Q-l,8- naphthyridine (I) or its tautomeric 4-hydroxy-7-Q-1,8- naphthyridine (IA) with a formylating agent to produce l,4-dihydro-4-oxo-7-Q-1,8-naphthyridine-3- carboxaldehyde (II) or its tautomeric 4-hydroxy-7-Q- l,8-naphthyridine-3-carboxaldehyde (HA) is carried out preferably by reacting I (or IA) with phosphorus oxyhalide and dimethylformamide to form the corresponding 3-dimethylformiminium halide, e.g.,

3CH=N (CH;,) Cl using phosphorus oxychloride, and

then making the reaction mixture alkaline to produce the corresponding 3CHO compound (II or IIA). The reaction is conveniently run by adding the phosphorus oxyhalide to a stirred mixture of l(or IA) and dimethylformamide. After the exothermic reaction subsides, the reaction mixture is gently heated, e.g., on a steam bath, to ensure completion of the reaction, cooled and poured into cold water and the resulting reaction mixture is made alkaline, e.g., using aqueous sodium or potassium hydroxide or the like, to convert the 3-dimethylformiminium halide to the 3-carboxaldehyde. Because of its ready availability and low cost, phosphorus oxychloride is preferably used. Alternatively, in place of phosphorus oxychloride there can be used phosphorus pentachloride, thionyl chloride, oxalyl chloride, phosphorus oxybromide, phosphorus tribromide, and the like. Also, in place ofdimethylformamide there can be used N-methyl-N-phenylformamide.

The reaction of l,4-dihydro-4-oxo-7-QJ,8- naphthyridine-3-carboxaldehyde (II) or its tautomeric 4-hydroxy-7-Q- l ,8-naphthyridine-3-carboxaldehyde (IIA) with a lower-alkylating agent to produce 1- (lower-alkyl)-l,4-dihydro-4-oxo-7-Q-I,8- naphthyridine-3-carboxaldehyde (III) is generally carried out by reacting said compound of formula II or IIA with a lower-alkyl ester of a strong inorganic acid or an organic sulfonic acid, said ester having the formula R,-An, where An is an anion of a strong inorganic acid or an organic sulfonic acid, e.g., chloride, bro mide, iodide, sulfate, methanesulfonate, benzenesulfonate, and para-toluenesulfonate, and R, is loweralkyl. This alkylation is preferably run using a slight excess of the alkylating agent although equimolar quantities give satisfactory results. The chloride, bromide or iodide is preferred because of the ready availability of the requisite lower-alkyl halides; and the reaction is carried out preferably in the presence of an acidacceptor. The acid-acceptor is a basic substance which preferably forms freely water-soluble by-products easily separable from the product of the reaction, including for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium alkoxides, potassium alkoxides, sodium amide, and the like. The acid-acceptor takes up the hydrogen halide (or HAn) which is split out during the course of the reaction. The reaction is preferably carried out in the presence of a suitable solvent which is inert under the reaction conditions, e.g., a solvent such as loweralkanol, acetone, dioxane, dimethylformamide, dimethyl sulfoxide, hexamethyl phosphoramide, or a mixture of solvents, e.g., a mixture of water and a lower-alkanol. The reaction is generally carried out at a temperature between about room temperature (about 2025C.) and C., preferably heating on a steam bath in a stirred mixture of dimethylformamide and anhydrous potassium carbonate.

The reaction of l-(lower-aIkyl)-I ,4-dihydro-4-oxo-7- Q-l,8-naphthyridine-3-carboxaldehyde (III) with an oxidizing agent to produce l-(lower-alkyl)-l ,4- dihydro-4-oxo-7-Q- l ,8-naphthyridine-3-carboxylic acid (IV) is generally carried out by reacting III with an oxidizingagent capable of converting formyl to carboxy. Such oxidizing agents are, for example, an alkali permanganate, e.g., KMnO in a basic or an acidic medium; an alkali dichromate, e.g., Na Cr O or chromic anhydride (CrO under acidic conditions, preferably using sulfuric acid; aqueous nitric acid, e.g., 2035% HNO and the like. The reaction conditions vary and are dependent upon the particular oxidizing agent used. For example, oxidation with potassium permanganate is conveniently run at low temperature, preferably below 20C., in a basic medium, preferably in pyridine which also acts as solvent or in aqueous sodium or potassium hydroxide solution or in aqueous sulfuric acid, preferably using about 2 moles of potassium permanganate per 3 moles of the 3-carboxaldehyde. Oxidation using nitric acid is conveniently run by heating a stirred mixture of the 3-carboxaldehyde with an excess of 30 percent nitric acid.

Alternatively, the 3-carboxaldehyde (III) can be converted to the 3-carboxylic acid (IV) via the 3-cyano compound.

The best mode contemplated for carrying out the invention is now set forth as follows:

EXAMPLE 1 l,4-Dihydro-7-methyl-4-oxo-l ,8-naphthyridine-3- carboxaldehyde is made alkaline with 30 ml. of 35% aqueous sodium hydroxide solution to convert the 3-dimethylformiminium chloride to the 3-carboxaldehyde. The alkaline solution is made acidic with 6N hydrochloric acid and the resulting precipitate is collected, washed with water, dried in vacuo at 60C. and is recyrstallized from dimethylformamide to yeild l,4-dihydro-7-methyl-4- oxo- 1 ,8 naphthyridine-3-carboxaldehyde.

EXAMPLE 2 l-Ethyl- 1 ,4-dihydro-7-methyl-4-oxol ,8-v naphthyridine-3-carboxaldehyde To a stirred suspension heated on a steam bath and containing 3.8 g. of 1,4-dihydro-7-methyl-4-oxo-1 ,8- naphthyridine-3-carboxaldehyde in 30 ml. of dimethylformamide is added 8.3 g. of anhydrous potassium carbonate and the mixture is stirred for about 15 minutes. To the stirred hot mixture is added 3.8 g. of ethyl iodide and the resulting mixture is stirred with heating on the steam bath for 90 minutes. The hot reaction mixture is poured into three volumes of ice water. The resulting precipitate is collected, triturated with warm water, washed sparingly with warm water and dried in vacuo at 60C. to yield l-ethyl-1,4-dihydro-7-methyl-4-oxol,8-naphthyridine-3-carboxaldehyde. When recrystallized successively from isopropyl alcohol and ethyl acetate, this compound melted at l86188C.

EXAMPLE 3 l-Ethyl-l ,4-dihydro-7-methyl-4-oxol ,8- naphthyridine-3-carboxylic acid A suspension of 3.3 g. of l-ethyl-l,4-dihydro-7- methyl 4-oxo-l,8-naphthyridine-3-carboxaldehyde in 35 ml. of pyridine and 7 ml. of water is stirred and cooled to 10C. in an ice bath. Solid potassium permanganate (7.5 g.) is added in small portions over the course of about 55 minutes. The temperature is not allowed to rise above C. and small amounts of water totalling 35 ml. is added during the course of the addition. The resulting mixture is stirred about 30 minutes longer at l020C. and then filtered through infusorial earth. The cake of collected manganese dioxide is washed with a little water and the combined filtrates are treated with saturated aqueous sodium bisulfite solution until the excess permanganate is destroyed. The solution is then acidified with excess 6N hydrochloric acid. After cooling in ice, the precipitated solid is collected by vacuum, rinsed with fresh water and sucked as dry as possible. The material is recrystallized from 18 ml. of dimethylformamide and dried for 18 hours in a vacuum oven (80C.). There is obtained, as pale yellow crystals, l-ethyl-l,4-dihydr0-7-methyl-4-oxo-l,8- naphthyridine-3-carboxylic acid, m.p. 232234C. A mixed melting point with authentic material is unde pressed.

This oxidation also is run as follows: A mixture of 2.5 g. of l-ethyl-1 ,4-dihydro-7-methyl-4-oxo-l ,8- naphthyridine-S-carboxaldehyde and 70 g. of 30% aqueous nitric acid is stirred vigorously on a steam bath until a test portion shows almost complete solubility in dilute aqueous sodium hydroxide solution. The reaction mixture is cooled, made alkaline with sodium hydroxide solution, washed with benzene, treated with decolorizing charcoal and filtered. The filtrate is slowly EXAMPLE4 7-Ethyl-l ,4-dihydro-4-oxo-l ,8-naphthyridine-3- carboxaldehyde using 7-ethy1-1,4-dihydro-4-oxo-1,8- naphthyridine.

EXAMPLES 1,4-Dihydro-4-oxo-7-n-propyl-l ,8-naphthyridine-3- carboxaldehyde using 1,4-dihydro-4-oxo-7-n-propyl- 1,8-naphthyridine.

EXAMPLE6 l,4-Dihydro-7-isobutyl-4-oxo-l ,8-naphthyridine-3- carboxaldehyde using l,4-dihydro-7-isobutyl-4-oxo- 1,8-naphthyridine.

EXAMPLE7 7-n-l-lexyl-1 ,4-dihydro-4-oxo-1 ,8-naphthyridine-3 carboxaldehyde using 7-n-hexyl-l,4-dihydro-4-oxo- 1,8-naphthyridine.

EXAMPLE 8 7-Acetoxymethyl-l ,4-dihydro-4-oxo-1 ,8- naphthyridine-3-carboxaldehyde using acetoxymethyl-l,4-dihydro-4-oxo-1,S-naphthyridine.

EXAMPLE9 l,4-Dihydro-4-oxo-7-propion0xymethyll ,8- naphthyridine-3-carboxaldehyde using 1,4-dihydro-4- oxo-7-propionoxymethyl-1,8-naphthyridine.

EXAMPLE 10 l,4-Dihydro-7-isobutyroxymethyl-4-oxo-1,8-

-naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- isobutyroxymethyl-4-oxo-l ,S-naphthyridine.

EXAMPLE 1 l 7-l-lexanoyloxymethyl- 1 ,4-dihydro-4-oxo-l ,8-

naphthyridine-3-carboxaldehyde using 7- hexanoyloxymethyl-l ,4-dihydro-4-oxol ,8- naphthyridine.

EXAMPLE l2 1,4-Dihydro-4-oxo-7-(4-pyridyl)-1,8-naphthyridine- 3-carboxaldehyde using pyridyl)-l ,8-naphthyridine.

EXAMPLE 13 1,4-Dihydro-4-oxo-7-(3-pyridyl)-1,8-naphthyridine- 3-carboxaldehyde using 1,4-dihydro-4-oxo-7-(3- pyridyl)-1,8-naphthyridine.

EXAMPLE 14 l,4-Dihydro-7-( 2-methyl-4-pyridyl)-4-oxo-l ,8- naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- (2-methyl-4-pyridyl)-4-oxo-1,8-naphthyridine.

' EXAMPLE 15 l,4-Dihydro-7-( 3-methy1-4-pyridyl)-l ,8-

naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- naphthyridine a molar equivalent quantity of the appropriate 1,4-dihydro-4-oxo-7-Q-1 ,8-naphthyridine, the compounds of Examples 4-19 are obtained:

(3-methy1-4-pyridyl)-4-oxo-1,8-naphthyridine.

EXAMPLE l6 7-(2-Ethyl-4-pyrid1y)-l ,4-dihydro-4-oxo-l ,8- naphthyridine-3-carboxaldehyde using 7-(2-ethyl-4- pyridyl)-1 ,4-dihydro- 4-oxol ,8-naphthyridine.

EXAMPLE 17 7-( 3-Ethyl-4-pyridyl l ,4-dihydro-4-oxol ,8- naphthyridine-3-carboxaldehyde using 7-(3-ethyl-4- pyridyl)-1,4-dihydro-4-oxo-1,S-naphthyridine.

EXAMPLE 18 1,4-Dihydro-7-(2,6-dimethyl-4-pyridyl )-4-oxol ,8- naphthyridine-3-carboxaldehyde using l,4-dihydro-7- (2,6-dimethyl-4-pyridyl)-4-oxo-1,8-naphthyridine.

EXAMPLE l9 1,4-Dihydro-7-( 3,5-dimethyl-4-pyridyl )-4-oxo-l ,8- naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- (3,5-dimethyl-4-pyridyl)-4-oxo1,S-naphthyridine.

Following the procedure described in Example 2 but using in place of 1,4-dihydro-7-methyl-4-oxo-1,8- naphthyridine-3-carboxaldehyde a molar equivalent quantity ofthe appropriate 1,4-dihydro-4-oxo-7-Q-1,8- naphthyridine-3-carboxaldehyde, the compounds of Examples 20-35 are obtained:

EXAMPLE 20 l ,7-Diethyl-l ,4-dihydro-4-oxo-1,8-naphthyridine-3- carboxaldehyde using 7-ethyl-l,4-dihydro-4-oxo-1,8- naphthyridine-3-carboxaldehyde. Similarly, using said 7-ethyl compound and a molar equivalent quantity of dimethyl sulfate, n-propyl iodide, isobutyl bromide or n-hexyl chloride in place of ethyl iodide, there is obtained 7-ethyl-1,4-dihydro-l-methyl-4-oxo-l,8- naphthyridine-3-carboxaldehyde, 7-ethyl-I,4-dihydro- 4-oxo-1-n-propyl-l,8-naphthyridine-3- carboxaldehyde, 7-ethyl-1,4-dihydro-l-isobutyl-4-oxol,8-naphthyridine-3-carboxaldehyde or 7-ethyl-1-nhexyl-l ,4-dihydro-4-oxo-l ,8-naphthyridine-3- carboxaldehyde, respectively.

EXAMPLE 21 l-Ethyl-l,4-dihydro-4-oxo-7-n-propyl-1,8- naphthyridine-3-carboxaldehyde using l,4-dihydro-4- oxo-7-n-propy1-1,8-naphthyridine-3-carboxaldehyde.

EXAMPLE 22 l-Ethyl-l,4-dihydro-7-isobutyl-4-oxo-1,8- naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- isobutyl-4-oxo-l ,8-naphthyridine-3-carboxa1dehyde.

EXAMPLE 23 l-Ethyl-7-n-hexyl-1,4-dihydro-4-oxo-1,8- naphthyridine-3-carboxaldehyde using 7-n-hexyl-1,4- dihydro-4-oxo-1,8-naphthyridine-3-carboxaldehyde.

EXAMPLE 24 7-Acetoxymethyl-l-ethyl-l,4-dihydro-4-oxo-1,8-

naphthyridine-3-carboxaldehyde using acetoxymethyl-l,4-dihydro-4-oxo-1,8-naphthyridine- 3carboxa1dehyde. Similarly, using said 7- acetoxymethyl compound and a molar equivalent quantity of dimethyl sulfate, n-propyl iodide, isobutyl bromide or n-hexyl chloride in place of ethyl iodide, there is obtained 7-acetoxymethyl-1,4-dihydro-1- methyl-4-oxo-l,8-naphthyridine-3-carboxaldehyde, 7- acetoxymethyl-1,4-dihydro-4-oxo-l-n-propyl-l ,8- naphthyridine-B-carboxaldehyde, 7-acetoxymethyl- 1,4-dihydrol-isobutyl-4-oxo-l ,8-naphthyridine-3- carboxaldehyde or 7-acetoxymethyl-l-n-hexyl-l,4-

8 dihydro-4-oxo-1,8-naphthyridine-3-carboxaldehyde, respectively.

EXAMPLE 25 l-Ethyl-l,4-dihydro-4-oxo-7-propionoxymethyl-1,8- naphthyridine-3-carboxaldehyde using 1.4-dihydro-4- oxo-7-propionoxymethyl-1 ,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 26 l-Ethyl-l,4-dihydro-7-isobutyroxymethyl-4-oxo-1,8- naphthyridine-3-carboxa1dehyde using 1,4-dihydro-7- isobutyroxymethyl-4-oxo-1,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 27 l-Ethyl-7-hexanoyloxymethyl-1,4-dihydro-4-oxol,8-naphthyridine 3-carboxaldehyde using hexanoyloxymethyl- 1 ,4-dihydro-4-oxol ,8- naphthyridine-3-carboxaldehyde.

EXAMPLE 28 EXAMPLE 3O l-Ethyl-l ,4-dihydro-7-( 2-methyl-4-pyridyl)-4-oxo- 1,8-naphthyridine-3-carboxaldehyde using dihydro-7-(2-methyl-4-pyridy1)-4-oxo-1,8- naphthyridine-3-carboxaldehyde.

EXAMPLE 31 l-Ethyl-1,4-dihydro-7-(3-methyl-4-pyridyl)-1,8- naphthyridine-3-carboxaldehyde using 1,4-dihydro-7- (3-methy1-4-pyridy1)-4-oxo-1,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 32 1-Ethyl-7-(2-ethy1-4-pyridyl)-1,4-dihydro-4-oxo-1,8-

naphthyridine-3-carboxaldehyde using 7-(2-ethyl-4- pyridyl)-1,4-dihydro-4-oxo-l,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 33 l-Ethyl-7-(3-ethyl-4-pyridyl)-1,4-dihydro-4-oxo-1,8- naphthyridine-3-ca1;boxaldehyde using 7-(3-ethyl-4- pyridyl )-1 ,4-dihydro-4-oxo-1,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 55 l,4-Dihydro-l-isobutyl-4-oxo-7-(4-pyridyl)- l ,8- naphthyridine-3-carboxylic acid using l,4-dihydro-lisobutyl-4-oxo-7-(4-pyridyl)-l ,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 56 l-n-Hexyl-l,4-dihydro-4-oxo-7-(4-pyridyl)-l,8- naphthyridine-3-carboxylic acid using l-n-hexyl-l,4- dihydro-4-oxo-7-(4-pyridyl)- l ,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 57 l-Ethyl-l,4-dihydro-4-oxo-7-(3-pyridyl)-l,8- naphthyridine-3-carboxylic acid using l-ethyl-l,4- dihydro-4-oxo-7(3-pyridyl)-l,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 58 l-Ethyl-l ,4-dihydro-7-( 2-methyl-4-pyridyl)-4-oxol,8-naphthyridine-3-carboxylic acid using l-ethyl-1,4- dihydro-7-( 2-methyl-4-pyridyl )-4-oxo-l ,8- naphthyridine-3-carboxaldehyde.

EXAMPLE 59 l-Ethyl-l,4-dihydro-7-(3-methyl-4-pyridyl)-l,8- naphthyridine-3-carboxylic acid using l-ethyl-l,4- dihydro-7-(3-methyl-4-pyridyl)-1,8-naphthyridine-3- carboxaldehyde.

EXAMPLE 6O l-Ethyl-7-(2-ethyl-4-pyridyl)-l,4-dihydro-4-oxo-l,8- naphthyridine-3-carboxylic acid using l-ethyl-7-(2- ethyl-4-pyridyl )-l ,4-dihydro-4-oxol ,S-naphthyridine- 3-carboxaldehyde.

EXAMPLE 6l l-Ethyl-7-( 3-ethyl-4-pyridyl l ,4-dihydro-4-oxo-l ,8- naphthyridine-3-carboxylic acid using l-ethyl-7-(3- ethyl-4-pyridyl l ,4-dihydro-4-oxo-l ,8-naphthyridine- 3-carboxaldehyde.

EXAMPLE 62 l-Ethyll ,4-dihydro-7-( 2,6-dimethyl-4-pyridyl)-4- oxo-l,8-naphthyridine-3-carboxylic acid using l-ethyll,4-dihydro-7-( 2,6-dimethyl-4-pyridyl )-4-oxo-l ,8- naphthyridine-3-carboxaldehyde.

EXAMPLE 63 l-Ethyl-l ,4-dihydro-7-( 3 ,5-dimethyl-4-pyridyl)-4- oxo-l,8-naphthyridine-3-carboxylic acid using l-ethyl- 1 ,4-dihydro-7-(3,5-dimethyl-4-pyridy1)-4-oxo-l ,8- naphthyridine-3-carboxaldehyde.

The following Examples 64-1 10 illustrate the preparation of the intermediate l,4-dihydro-4-oxo-7-Q-l,8- naphthyridines, said preparation being disclosed and claimed in copending US. Pat. application Ser. No. 335,733.

EXAMPLE 64 Cyclic isopropylidenyl N-( 6-methyll-oxo-2-pyridyl )aminomethylenemalonate To a solution containing 26.2 g. of cyclic isopropylidenyl N-(6-methyl-2-pyridyl)aminomethylenemalonate in 150 ml. of chloroform is slowly added with stirring 19 g. of 3-chloroperbenzoic acid, keeping the reaction temperature below about 40C. After the addition is completed, the reaction mixture is heated on a steam bath for about 30 minutes. The reaction mixture is extracted successively with 50 ml. of ice cold l0% aqueous potassium bicarbonate solution, ml. of water, 30 ml. of ice cold 10% aqueous potassium bicarbonate solution and 25 ml. of water. The resulting chloroform solution is washed with water, dried over anhydrous potassium carbonate, filtered and the filtrate concentrated in vacuo to remove the chloroform. The remaining solid is triturated with isopropyl alcohol and then recrystallized from ethanol using decolorizing charcoal to yield cyclic isopropylidenyl N-(6-methyl-l-oxo-2- pyridyl)aminomethylenemalonate, m.p. 222223C. with decomposition.

The above preparation also is carried out using a molar equivalent quantity of other oxidizing agents in a suitable solvent inert under the reaction conditions, e.g., use of peracetic acid in acetic acid.

EXAMPLE 65 l,4-Dihydro-7-methyl-4-oxo-1,8-naphthyridine-8- oxide To a ml. portion of diethyl phthalate heated to 275C. is added with stirring 2.78 g. of cyclic isopropylidenyl N-(6-methyl-l-oxo-2-pyridyl)aminomethylenemalonate. The stirred reaction mixture is heated at the same temperature for 2 minutes and then allowed to cool to room temperature. The precipitated solid is collected, washed well with ether and air-dried to yield the product, l,4-dihydro-7-methyl-4-oxo-l,8- naphthyridine-S-oxide, which is tautomeric with 4- hydroxy-7-methyl-l,8-naphthyridine-8-oxide. Recrystallization, if desired, is carried out using dimethylformamide.

The above cyclization also is carried out in 225 ml. of refluxing Dowtherm A in place of the diethyl phthalate.

EXAMPLE 66 l,4-Dihydro-7-methyl-4-oxo-1,8-naphthyridine A mixture containing 8.75 g. of l,4-dihydro-7- methyl-4-oxo-l,8-naphthyridine-8-oxide, 250- ml. of absolute ethanol and 5 g. of Raney nickel is hydrogenated at about 25C. in a Parr apparatus using an initial pressure of 55 p.s.i. of hydrogen. The catalyst is filtered off, the filtrate treated with decolorizing charcoal and filtered, and the filtrate concentrated in vacuo and chilled. The precipitate is collected, recrystallized from ethanol and dried over P 0 at 25C. overnight to yield 1,4-dihydro-7-methyl-4-oxo-l ,S-naphthyridine, m .p. 235-236C. When recrystallized from water and dried, this compound melted at 235-237C.

Following the procedure described in Example 64 but using in place of cyclic isopropylidenyl N-(6- methyl-2-pyridyl)aminomethylenemalonate a molar equivalent quantity of the appropriate cyclic alkylidenyl N-(6-Q-2-pyridyl)aminomethylenemalonate, the compounds of Examples 67-81 are obtained:

EXAMPLE 67 Cyclic isopropylidenyl N-(6-ethyl-l-oxo-2-pyridyl- )aminomethylenemalonate using cyclic isopropylidenyl N-'(6-ethyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amin0-6-ethylpyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 68 Cyclic isopropylidenyl N-(l-oxo-6-n-propyl-2- pyridyl)aminomethylenemalonate using cyclic isopropylidenyl N-(6-n-propyl-2-pyridyl)aminome thylenemalonate, the latter prepared by reacting 2-amino-6-n-propylpyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 69 Cyclic isopropylidenyl N-(6-isopr0pyl-l-oxo-2 pyridyl)aminomethylenemalonate using cyclic isopropylidenyl N-(6-isopropyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2 -amino-6-isopropylpyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 70 Cyclic isopropylidenyl N-(6-n-butyl-l-oxo-2-pyridyl- )aminomethylenemalonate using cyclic isopropylidenyl N-(6-n-butyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amino-6-n-butylpyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 7l Cyclic isopropylidenyl N-(6-n-hexyl-l-oxo-2-pyridyl- )aminomethylenemalonate using cyclic isopropylidenyl N-(6-n-hexyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amino-6-n-hexylpyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 72 Cyclic 3-pentylidenyl N-( 6 -methyll -oxo-2-pyridyl- )aminomethylenemalonate using cyclic 3-pentylidenyl N-(6-methyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amino-6-methylpyridine with a mixture of triethyl orthoformate and cyclic 3- pentylidenyl malonate.

EXAMPLE 73 Cyclic Z-butylidenyl N-(6-methyl-l-oxo-2-pyridyl- )aminomethylenemalonate using cyclic 2-butylidenyl N-(6-methyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amino-6-methylpyridine with a mixture of triethyl orthoformate and cyclic 2- butylidenyl malonate.

EXAMPLE 74 Cyclic 4-heptylidenyl N-(6-methyl-l-oxo-2-pyridyl- )aminomethylenemalonate using cyclic 4-heptylidenyl N-(6-methyl-2-pyridyl)aminomethylenemalonate, the latter prepared by reacting 2-amino-6-methylpyridine with a mixture of triethyl orthoformate and cyclic 4- heptylidenyl malonater EXAMPLE 75 Cyclic isopropylidenyl N-[l-oxo-6-(1-oxo-4- pyridyl)-2-pyridyl]aminomethylenemalonate using cyclic isopropylidenyl N-[6-(4-pyridyl)-2-pyridyl- ]aminomethylene-malonate, the latter prepared by reacting 2-amino-6-(4-pyridyl)-pyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 76 Cyclic isopropylidenyl N-[ 1-0x0-6-( l-oxo-3- pyridyl)2-pyridyl]aminomethylenemalonate using cyclic isopropylidenyl N-[6-(3-pyridyl)-2-pyridyl- ]aminomethylenemalonate, the latter prepared by reacting 2-amino-6-(3-pyridyl)pyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 77 Cyclic isopropylidenyl N-[1-oxo-6-(2-methyl-1-0xo- 4-pyridyl)-2-pyridyl]aminomethylenemalonate using cyclic isopropylidenyl N-[6-(2-methyl-4-pyridyl)-2- pyridyl]aminomethylenemalonate, the latter prepared by reacting 2-amin0-6-(2-methyl-4-pyridyl)pyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 78 Cyclic isopropylidenyl N-[l-ox0-6-(2-ethyl-l-oxo-4- pyridyl)-2-pyridyl]aminomethylenemalonate using cyclic isopropylidenyl N-[ 6-(2-ethyl-4-pyridyl)-2-pyridyl- ]aminomethylenemalonate, the latter prepared by reacting 2-amino-6-(2-ethyl-4-pyridyl)pyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

' EXAMPLE 79 Cyclic isopropylidenyl N-[l-oxo-6-(3-ethyl-lox0-4- pyridyl)-2-pyridyl]aminomethylenemalonate using'cyclic isopropylidenyl N-[6-(3 ethyl-4-pyridyl)-2-pyridyl- ]aminomethylenemalonate, the latter prepared by reacting 2-amino-6-(3-ethyl-4-pyridyl)pyridine with a mixture of triethyl orthoformate and cyclic isopropylidenyl malonate.

EXAMPLE 8O 'Cyclic isopropylidenyl N-[l-oxo-6-(2,6-dimethyl-loxo-4-pyridyl)-2-pyridyl]aminomethylenemalonate using cyclic isopropylidenyl N-[6-(2,6-dimethyl-4- pyridyl)-2-pyridyl]aminomethylenemalonate, the latter prepared by reacting 2-amino-6-(2,6-dimethyl-4- pyridyl)pyridine with a mixture of triethyl orthofor mate and cyclic isopropylidenyl malonate.

EXAMPLE 8l EXAMPLE 82 7-Ethyl-l ,4-dihydro-4-oxo-l ,8-naphthyridine-8- oxide using cyclic isopropylidenyl N-(6-ethyl-l-oxo-2- pyridyl)aminomethylenemalonate.

EXAMPLE 106 l,4-Dihydro-4-oxo-7-(3-methyl-4-pyridyl)-1,8- naphthyridine using l,4-dihydr-4-oxo-7(3-methyl-loxo-4-pyridyl l ,8-naphthyridine-8-oxide.

EXAMPLE 107 1,4-Dihydr0-4-oxo-7-(2-ethyl-4-pyridyl)-l ,8-

naphthyridine using l,4-dihydro-4-oxo-7-(2-ethyl-loxo-4-pyridyl )-l ,8-naphthyridine-8-oxide.

EXAMPLE 108 l,4-Dihydro-4-oxo-7-( 3-ethyl-4-pyridyl )-l ,8- naphthyridine using l,4-dihydro-4-oxo-7-( 3-ethyl- 1 oxo-4-pyridyl l ,8-naphthyridine-8-oxide.

EXAMPLE 109 l ,4-Dihydro-4-oxo-7-(2,6-dimethyl-4-pyridyl)-1,8- naphthyridine using l,4-dihydro-4-oxo-7-(2,6- dimethyll oxo-4-pyridyl )-l ,8-naphthyridine-8-oxide.

EXAMPLE llO phosphorus pentachloride, thionyl chloride, oxalyl chloride or phosphorus tribromide and dimethylformamide or Nmethyl-N-phenylformamide followed by alkaline hydrolysis of the resulting 3-formiminium halide to produce 1,4-dihydro-4-oxo-7-Q-l ,8- naphthyridine-3-carboxaldehyde, reacting the latter with a lower-alkylating agent to produce l-(loweralkyl )-1 ,4-dihydro-4-oxo-7-Q- 1 ,8-naphthyridine-3- carboxaldehyde, and reacting said l-(lower-alkyl)-3- carboxaldehyde with an oxidizing agent capable of converting CHO to COOH to produce l-(loweralkyl l ,4-dihydro-4-oxo-7-O- l ,8-naphthyridine-3- carboxylic acid, where Q is lower-alkyl, loweralkanoyloxymethyl, 4(or 3)-pyridyl or 4(or 3)-pyridyl having one or two lower-alkyl substituents.

2. The process consisting of reacting 1,4-dihydro-4- oxo-7-Ql,8-naphthyridine with phosphorous oxyhalide, phosphorus pentachloride, thionyl chloride, oxalyl chloride or phosphorus tribromide and dimethylformamide or N-methyl-N-phenylformamide followed by alkaline hydrolysis of the resulting 3-formiminium halide to produce l,4-dihydro-4-oxo-7-Q-l,8- naphthyridine-3carboxaldehyde, where Q is loweralkyl, lower-alkanoyloxymethyl, 4(or 3)-pyridyl or 4(or 3)-pyridyl having one or two lower-alkyl substituents.

3. The process according to claim 1 where Q is methyl and the lower-alkylating agent is an ethylating agent to produce l-ethyl-l,4-dihydro-7methyl-4-oxo l,8uaphthyridine-S-carboxylic acid.

4. The process according to claim 2 where Q is methyl. 

1. THE PROCESS CONSISTING OF REACTING 1,4-DIHYDRO-4-OXO-7Q-1,8-NAPHTHYRIDINE WITH PHOSPHURUS OXYHALIDE, PHOSPHURUS PENTACHLORIDE, THIONYL CHLORIDE, OXALYL CHLORIDE, PHOSPHORUS TRIBROMIDE AND DIMETHYLFORMAMIDE OR N-METHYL-NPHENYLFOEMIMINUM FOLLOWED BY ALKALINE HYDROLYSIS OF THE RESULTING 3-FORMIMINUM HALIDE TO PRODUCE 1,4-DIHYDRO-4-OXO-7-Q1,8-NAPHTHYRIDINE-3-CARBOXALDEHYDE, REACTING THE LATTER WITH A LOWER-ALKYLATING AGENT TO PRODUCE 1-(LOWER ALKYL)-1,4DIHRO-4-OXO-7-Q-1,8-NAPHTHYRIDINE-3-CARBOXALDEHYDE, AND REACTING SAID 1-(LOWER-ALKYL)-3-CARBOXALDEHYDE WITH AN OXIDIZING AGENT CAPABLE OF CONVERTING -CHO TO -COOH TO PRODUCE 1-(LOWER-ALKYL)-1,4-DIHYDRO-4-OXO-7-Q-1,8NAPHTHYRIDINE-3-CARBOXYLIC ACID, WHERE Q IS LOWER-ALKYL, LOWER-ALKANOYLOXYMETHYL, 4(OR 3)-PYRIDYL OR 4(OR 3)-PYRIDYL HAVING ONE OR TWO LOWER-ALKYL SUBSTUTIENTS.
 2. The process consisting of reacting 1,4-dihydro-4-oxo-7-Q-1,8-naphthyridine with phosphorous oxyhalide, phosphorus pentachloride, thionyl chloride, oxalyl chloride or phosphorus tribromide and dimethylformamide or N-methyl-N-phenylformamide followed by alkaline hydrolysis of the resulting 3-formiminium halide to produce 1,4-dihydro-4-oxo-7-Q-1,8-naphthyridine-3-carboxaldehyde, where Q is lower-alkyl, lower-alkanoyloxymethyl, 4(or 3)-pyridyl or 4(or 3)-pyridyl having one or two lower-alkyl substituents.
 3. The process according to claim 1 where Q is methyl and the lower-alkylating agent is an ethylating agent to produce 1-Ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naphthyridine-3-carboxylic acid.
 4. The process according to claim 2 where Q is methyl. 